Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a recording medium using a developer.
Description of the Related Art
Conventionally, there have been known in-line color system image forming apparatuses that primarily transfer toner images from a plurality of process cartridges onto an intermediate transfer belt to form an image on a sheet. In such image forming apparatuses, electrostatic latent images formed on photosensitive drums are developed by developing apparatuses to form toner images on the photosensitive drums in a plurality of process cartridges. Further, the toner images formed on the photosensitive drums are primarily transferred onto an intermediate transfer belt, and the toner images primarily transferred onto the intermediate transfer belt are then secondarily transferred onto a sheet. After that, the toner images secondarily transferred onto the sheet are heated and pressed by a fixing apparatus to be fixed onto the sheet. Thus, a color image is formed on the sheet.
Here, the image formed on the sheet needs to have a tinge and density as intended by a user. In addition, in color images formed by color image forming apparatuses, high tinge accuracy and tinge stability become important. Therefore, according to a technology disclosed in Japanese Patent Application Laid-open No. H8-227222, a bias applied to a developing roller and a rotation speed of the developing roller are changed to obtain a desired image tinge and image density. For example, the bias applied to the developing roller is increased to increase density of a toner image formed on a photosensitive drum and change a tinge of an image. In addition, the rotation speed of the developing roller is decreased to increase density of a toner image formed on the photosensitive drum and change a tinge of an image.
Further, according to a technology disclosed in Japanese Patent Application Laid-open No. 2013-210489, a rotation speed of a photosensitive drum is made slower than that of a developing roller to prevent rough feelings on an image formed on a sheet. In addition, magnetic flux density of a magnet provided inside the developing roller is increased to prevent a resin carrier from adhering to the photosensitive drum and prevent a problem from occurring in an image formed on the sheet.
Conventionally, as a method for detecting a residual amount of toner inside a developing apparatus, there has been known a method for detecting a residual amount of toner using image information received by an image forming apparatus. Specifically, first, the number of dots developed as a toner image may be acquired from image information (digital data) received by the image forming apparatus. Further, the number of the developed dots may be multiplied by an amount of the toner consumed to develop one dot to calculate an amount of the toner consumed by one image. Further, the amount of the consumed toner may be subtracted from a residual amount of the toner inside the developing apparatus to derive a residual amount of the toner after an image forming operation. Here, the amount of the toner consumed to develop one dot is stored in advance in a storage medium such as a memory.
However, the amount of the toner consumed to develop one dot changes when the bias applied to the developing roller and the rotation speed of the developing roller are changed as disclosed in Japanese Patent Application Laid-open No. H8-227222 and Japanese Patent Application Laid-open No. 2013-210489. Therefore, the amount of the toner consumed to form one image also changes, which results in an error in the residual amount of the toner after the image forming operation.